Field of the Invention
The present invention relates to an object information acquiring apparatus.
Description of the Related Art
The development of photoacoustic tomography (PAT) systems, in which information on body functions is obtained using light and ultrasonic waves, has proceeded in the field of health care in recent years for use as apparatuses that enable non-invasive imaging of the interior of the body.
Photoacoustic tomography refers to a technology for acquiring images of internal tissue serving as a generation source of acoustic waves by using photoacoustic effects in which pulsed light generated from a light source is irradiated onto an object and acoustic waves (and typically, ultrasonic waves) are generated by absorption of light that has propagated and diffused within the object. Changes in the received acoustic waves over time are detected at a plurality of locations, and the resulting signals are subjected to mathematical analysis processing, namely reconfiguration, thereby enabling information relating to optical properties, such as the absorption coefficient within the object, to be visualized three-dimensionally.
For example, in the case of using near infrared light for the pulsed light, since near infrared light easily passes through water that composes a major portion of the body, it has the property of being easily absorbed by hemoglobin present in blood. Consequently, images of blood vessels can be obtained by visualizing absorption coefficients calculated based on acoustic waves generated by near infrared light. As a result, this technology is expected to be used to acquire images of and detect neovascularization frequently present around tumors.
Moreover, by comparing and arithmetically processing images of blood vessels obtained with pulsed light of different wavelengths, the ratio of oxyhemoglobin to total hemoglobin in blood, namely oxygen saturation, can be measured. Since blood surrounding malignant tumors is thought to have lower oxygen saturation than blood surrounding benign tumors, determination of oxygen saturation is expected to make it possible to distinguish between malignant and benign tumors. In addition, by selecting a suitable wavelength of pulse light, the presence ratios of substances composing an object can be determined using the same principle.
In addition, ultrasound examination apparatuses are apparatuses that convert information on body functions to images by receiving acoustic waves in the same manner as photoacoustic tomography. Ultrasound examination apparatuses acquire images by transmitting acoustic waves to the body and receiving acoustic waves that have been reflected in the body. Acoustic waves have the property of being reflected at an interface that has different acoustic impedance defined as the product of the propagation speed and density of the acoustic waves, and ultrasound examination apparatuses enable visualization of the distribution of acoustic impedance in the body.
In addition, when measuring an object in which there is movement such as blood flow, analyzing the frequency of the reflected waves makes it possible to determine the flow rate and direction thereof. Since this technique is referred to as the color Doppler method, the resulting flow rate and direction are referred to as color Doppler information.
A technique in which three-dimensional data is projected onto a two-dimensional flat surface is used as a method for displaying three-dimensional data obtained with an apparatus on a two-dimensional display. For example, an example of that technique is maximum intensity projection (MIP), in which the maximum value of voxels on the axis in the projecting direction is displayed on the projection plane. In the case of an object having a three-dimensionally complex shape as represented by blood vessels, although it is difficult to ascertain the overall structure if only a certain cross-section is displayed, displaying by MIP makes it easier to interpret three-dimensional shapes of blood vessels on a two-dimensional display.
In U.S. Pat. No. 6,205,350, a second set of three-dimensional data, for which structural information has been enhanced, is acquired from a first set of three-dimensional data obtained by measurement. The second set of three-dimensional data is projected onto a two-dimensional flat surface using voxels of the first set of three-dimensional data at the same coordinates as the contributing voxels when projected on a two-dimensional flat surface.
Patent Literature 1: U.S. Pat. No. 6,205,350